Spring-set air-release parking brakes are commonly utilized in trailers and heavy-duty over-the-road highway trucks and the like. These brakes utilize large heavy-duty coil springs to preset the brakes in a normally-locked condition and are released by air pressure.
Quick-release valves are commonly employed in these spring-set air-release parking brake systems. A typical prior art quick-release valve 10 is shown in a non-pressurized state in FIG. 1 and is discussed at this point as background for the present invention.
The valve 10 permits air under pressure to enter the valve 10 at an inlet 12. The pressurized air at the inlet 12 deforms or flexes the periphery of a diaphragm 14 downwardly (as viewed in FIG. 1), sealing exhaust port 19 and permitting air to flow from the inlet 12 to outlets 16 which are in fluid communication with parking brake chambers 18, also referred to as spring-brake chambers 18. When the pressure in the chambers 18 is larger than the pressure at the inlet 12, the diaphragm 14 is flexed or deformed upwardly, sealing inlet 12 and allowing air within the chambers 18 to escape through the outlets 16, under the deformed central portion of the diaphragm 14, and out the exhaust port 19. The exhaustion of air from chambers 18 continues until the respective pressures on each side of diaphragm 18 are substantially equalized, assuming that the effective areas on each side are substantially equal.
Although the prior quick-release valves perform their primary function, i.e., assisting in the quick release of the air from the chambers of the parking brakes to effectuate quick setting of the parking brakes, such valves operate in an inefficient manner. For example, the compressors in the prior systems, rather than being in continual operation, have duty cycles in which they are deactivated when the system air pressure exceeds a first predetermined level, e.g., about 120 psi, and are reactivated when the system air pressure falls below a second predetermined level, e.g., about 90 psi. (The pressures referred to herein are gauge pressures.)
The system air pressure thus typically varies through a cycle from about 120 psi to about 90 psi. As the system air pressure rises from about 90 psi, and as above indicated, the periphery of the diaphragm 14 is deflected downwardly, permitting air to flow from the compressor to the parking brake chambers 18. As pressure in the system inlet falls from about 120 psi to about 90 psi, the central portion of the diaphragm moves upwardly exposing the exhaust port and permitting the air in the brake chambers to escape through the exhaust port 19.
Thus, such prior quick-release valves are beset with one or more of the following shortcomings:
a) The continual flexing of the diaphragm into various modes as the system air pressure cycles between about 90 and about 120 psi causes fatigue of the diaphragm in the quick release valve as well as other affected components in the brake system, such as the diaphragm and center seal of the spring brake chamber, leading to premature failures;
b) Energy is needlessly consumed, and thus wasted, from operating the compressor to recharge the spring-brake chambers from about 90 psi to about 120 psi as the system pressure rises during the actuation of the compressor;
c) The compressor has excessive wear and reduced life due to the added air demands to systematically fill and refill the spring-set brake chambers during each compressor activation/deactivation cycle; and
d) Objectionable noise occurs as the air is exhausted from the spring-set brake chambers when the inlet pressure drops from about 120 psi to about 90 psi or lower.
These and related problems have been recognized and solutions thereto proffered. Some background, for example, is set forth in U.S. Pat. No. 4,191,428, issued Mar. 4, 1980. Some solutions have been implemented, but the solutions have added complexity and costs, including additional components, increased assembly time, higher maintenance costs, and increased inventory burdens, both for manufacture and repair.